Bearing fits
A radial ball bearing on a turning shaft under a normal load takes a k5 shaft and an H7 housing: the inner ring, which the load rotates relative to, is gripped, and the outer ring may slide. Pick the bearing type, the load and the ring the load rotates relative to, enter the bore and OD, and both seats are worked out from the ISO 286 classes and the bearing’s own ring tolerances, and drawn.
Radial ball, normal load, load rotating relative to the inner ring: k5 shaft, H7 housing. Ring tolerances ISO 492 Normal class.
- Inner ring on the k5 shaft: press fit
- −21 to −2µm
- Outer ring in the H7 housing: slip (clearance) fit
- 0 to +43µm
- Shaft Ø k5, max / min
- Housing Ø H7, max / min
- Bore Δdmp, Normal class
- 0 / −10µm
- OD ΔDmp, Normal class
- 0 / −13µm
How it’s calculated
The shaft and housing limits are the nominal plus their ISO 286 deviations; the inner ring's bore (Normal class, Δdmp) is the hole on the shaft, and the housing is the hole on the outer ring's OD (ΔDmp). The largest clearance is the hole's upper limit less the shaft's lower, the smallest the hole's lower less the shaft's upper: both positive is a clearance fit, both negative an interference, one of each a transition.
| Bearing type | Ring | Load | Load case | Shaft tol | Housing tol |
|---|---|---|---|---|---|
| Radial Ball | inner | normal | Load rotates relative to the inner ring | k5 | H7 |
| Radial Ball | inner | normal | Load stationary relative to the inner ring | h6 | N7 |
- The ring the load rotates relative to takes the interference fit; the other ring is a sliding fit (g6 shaft where the inner ring must float axially, h6 otherwise).
- Indicative for shafts of about 18–100 mm: solid steel shaft, cast-iron or steel housing. Manufacturer tables band the shaft class by diameter, so confirm with the bearing maker’s table.
- For a load rotating relative to the outer ring, a thin-walled housing or heavy shock load takes P7; light-alloy housings need a tighter fit than listed.
Why do bearing fits depend on which ring rotates?
The ring the load rotates relative to needs the interference: a shaft-rotating machine with a fixed load direction takes a tight shaft fit and an H7 housing, and the reverse holds when the load rotates relative to the outer ring (M7 to N7 housing, g6 or h6 shaft). A slipping fit under the rotating load creep-walks the ring and destroys the seat, which is why the recommendation tables key on load case first, then load (light up to 0.06 Cr, normal to 0.12 Cr) and shaft diameter. Bearing manufacturers’ catalogs remain the authority for a specific bearing series and load — treat these values as the customary starting point for 18–100 mm shafts.